There is an overall need in molded parts, particularly in automotive applications such as bumpers, fender extensions, hub caps, and other fascia components and molded exterior parts, for products that have high gloss, good weatherability, high impact strength and high temperature properties (e.g., tensile strength and dimensional stability such as sag and creep resistance). It is also desirable to be able to mold in solid and metallic colors and, optionally, to be able to paint the parts. "Solid" colors present a homogenous finish, even at very close inspection. All ingredients, which can be substantial in number, are milled and blended such that, when applied, they appear to have been produced from a single, homogenous ingredient. The solid color does not sparkle or brighten when directly illuminated by a light source, nor does it appear to change significantly when viewed from different angles. "Metallic" colors (including pearlescents) contain discrete flake pigments, which can range from pearl flakes to aluminum flakes or mica flakes. These flakes are large enough to be discretely identifiable within the field of color being observed. The metallic color has a noticeable "sparkle" when the surface is directly illuminated with a light source, plus they appear to change in color as the panel is rotated from a perpendicular angle to an oblique one. This property is called "polychromaticity". This change in color as the viewing angle is rotated is also referred to as "travel" or "flop".
BEXLOY.RTM.W automotive engineering resin, a blend of ionomer and polyethylene reinforced by glass fiber, marketed by E. I. du Pont de Nemours and Company, has found increasing use in molded parts such as automobile bumpers because it satisfies most of these needs. Its benefits include good gloss (appearance), moderate mar resistance, good processibility and high impact strength at relatively low cost. Solid color can be incorporated into the material, but success in incorporating metallic colors has been limited. Also, paint adherence to BEXLOY.RTM.W resin is poor and paint application that requires use of high temperature paint baking ovens (Original Equipment Manufacturing "OEM" Painting) is not feasible since BEXLOY.RTM.W lacks suitable high temperature properties.
For applications such as automobile fascia (bumpers, for example), a mar resistance greater than that inherent in BEXLOY.RTM.W resin is needed. Thus, when using BEXLOY.RTM.W resin, a light grain is typically applied to the surface to enhance mar resistance. Any graining, however light and glossy, substantially retards the "Distinctness of Image" (DOI), a key index used to evaluate the perceived quality of an exterior finish in the automotive industry. DOI, a measure of the "crispness" or "degree of definition" of a reflection of a object in a colored finish compared to the actual object itself, is measured from the angle of reflection of a light beam from a spherical surface. DOI can be measured by a Hunterlab Model No. D47R-6F Doigon Gloss Meter. The test panel is placed on the instrument sensor and the sharpness of the reflected image is measured. Details of the DOI test procedure are described in GM Test Specification TM-204-M. In the automotive industry, satisfactory finishes on a smooth or "Class A" surface typically will have a finish with a DOI value of at least 60, preferably 80 or higher. A commercial, lightly-grained BEXLOY.RTM.W resin fascia used on a Neon automobile has a DOI of 0.
While still retaining other important performance characteristics, there is a need for higher gloss (at least a value of 60 when measured at 20.degree., and at least 75 when measured at 60.degree.) and higher DOI (at least 60), faster processing, better high temperature properties, and improved mar resistance without the need of light graining. Also, there is a need for being able to incorporate metallic colors and, alternatively, to be able to paint the molded part.
Certain blends of ionomers with polymers other than polyethylene (polyamides, for example) are known in the art. These prior art blends with nylon would not be suitable for the solving the problems experienced with BEXLOY.RTM.W resin, however.
U.S. Pat. No. 4,335,223 to Flood, et al., for example, teaches enhancing the notched Izod impact resistance of molded objects made from 50 to 99 wt. % nylon 6 or nylon 66 blended with an .alpha.-olefin/.alpha.,.beta.-ethylenically-unsaturated C.sub.3 -C.sub.8 carboxylic acid ("ethylene-acid copolymers") by adding 0.05 to 1 wt. % selected metal compounds such as antimony oxide and magnesium oxide.
U.S. Pat. No. 3,845,163 to Murch, another example, teaches improving weld-line toughness of blends of polyamide with ethylene-acid copolymers by neutralizing at least 10 percent of the acid groups with metal ions such as sodium, calcium and zinc in solid or aqueous solution form. Polyamide hydrolysis would be expected to result with the use of aqueous solution. Melt blending in conventional equipment and solution blending or dry mixing followed by extrusion or injection molding are taught. No preference for high intensity mixing is suggested. U.S. Pat. No. 3,845,163 teaches blends containing at least 50 weight percent (wt. %) polyamide (60-85 wt. % is claimed and 80 wt. % exemplified). While a wide range of acid level and degree of neutralization are disclosed, the highest acid level used in the reference is 12 wt. % and the highest neutralization is 76%.
Blends of polyamide and ionomer wherein the ionomer is the major component but the polyamide is the continuous or co-continuous phase have been made by employing compatibilizing agents. U.S. Pat. No. 5,091,478 to Saltman, for example, teaches blends of 25-50 volume % polyamide with ionomer employing polymeric grafting agents containing certain reactive groups. Preferred grafting agents are copolymers derived from ethylene/n-butyl acrylate/glycidyl methacrylate and ethylene/glycidyl methacrylate.